In known units for transferring a group of cigarettes from a seat on a continuous supply conveyor to a corresponding seat on a continuous wrapping wheel, as described for example in British Patent No. 1,203,259, the supply conveyor is normally defined by a chain or belt conveyor, the seats of which are fed along a path having one portion--hereinafter referred to as the "transfer portion" --which reproduces a portion of the circular path along which the seats on the wrapping wheel are fed. Along the transfer portion, the seats on the supply conveyor are moved in time, and maintained coaxial, with the corresponding seats on the wrapping wheel to transfer the group of cigarettes axially between two corresponding coaxial seats.
Axial transfer involves several drawbacks by subjecting the group of cigarettes to fairly severe mechanical stress (especially on modern packing machines capable of producing over ten packets a second) which may result in deformation of the cigarettes or tobacco fallout.
Axial transfer also requires that the supply conveyor and wrapping wheel be positioned side by side, i.e. in two different planes, which therefore increases the overall depth of the transfer unit and complicates control and maintenance.
Finally, the need for a common path portion defined by said transfer portion--between the wrapping wheel and the supply conveyor makes for a highly rigid arrangement of the conveyors, and calls for an extremely long and therefore bulky, high-cost chain or belt, as shown clearly by the device described in British Patent No. 1,203,259. A shorter chain or belt may be used, but only on condition that it be fed along a much more tightly curving path, thus subjecting the chain or belt to extremely severe mechanical stress.
EP Patent No. 548,978 discloses a unit for continuously transferring a group of cigarettes between relevant seats of two wrapping wheels. At a given transfer zone the seats on the two wheels are maintained facing and parallel to each other and to a fixed direction--in particular, a direction perpendicular to the respective axes of rotation of the wheels--by moving, in particular oscillating, the seats continuously with respect to the respective wheels.